Mix together the flour, sugar, baking powder, baking soda and salt and set aside. In a separate bowl, combine the egg yolks, oil, buttermilk, lemon zest and vanilla extract.

Make a well in the center of the dry ingredients and pour in the liquid mixture. Mix together until flour is just incorporated.
In a small bowl, beat egg whites and cream of tartar until soft peaks form. Fold the egg whites into the batter just until incorporated. Let set for 15 minutes and gently fold in the blueberries.

Heat a nonstick pan or cast iron griddle over medium heat. Brush with the butter and heat until the butter just begins to sizzle. Scoop scant 1/4 cup of the batter into the pan or onto the griddle and cook until bubbles appear on the top surface and the bottom is golden brown, about 1 to 1 1/2 minutes. Flip over and cook until the bottom is lightly golden brown, about 45 seconds. Remove to a baking sheet and keep warm in a low oven.

Combine blueberries, sugar, butter, vanilla bean and cinnamon stick in a small saucepan and bring to a boil over high heat. Reduce heat and simmer to dissolve sugar. Remove from the heat and stir in the cassis. Serve at room temperature, folding in the chopped mint just before serving.